The present invention relates generally to diamond particles and more particularly to increasing their compressive fracture strength and improving their oxidation resistance by thermally diffusing boron (B) into the top layer of the diamond crystal.
Its hardness and thermal properties are but two of he characteristics that make diamond useful in a variety of industrial components. Initially, natural diamond was used in a variety of abrasive applications. With the ability to synthesize diamond by high pressure/high temperature (HP/HT) techniques utilizing a catalyst/sintering aid under conditions where diamond is the thermodynamically stable form of carbon phase, a variety of additional products found favor in the marketplace. HP/HT conditions typically comprehend conditions such that the diamond is thermodynamically stable. Typically, this includes a temperature in the range of about 1500.degree. to 2700.degree. C. and a pressure in the range of about 5 to 20 GPa. Polycrystalline diamond compacts, often supported on a WC support in cylindrical or annular form, extended the product line for diamond additionally. However, the requirement of high pressure and high temperature has been a limitation in product configuration, for example. Of more recent vintage, is the low-pressure growth of diamond, dubbed "chemical vapor deposition" or "CVD" in the field. Additional product configuration is permitted by this diamond growth technique.
Regardless of whether the diamond is natural or synthetic, and regardless of the manner in which the synthetic diamond has been grown, diamond suffers from being unstable at elevated temperature. As the art is well aware, processing of diamond at temperatures of above 600.degree. to 700.degree. C. requires an inert atmosphere; otherwise, the diamond will oxidize. Thus, the ability to increase the oxidation resistance of diamond would be welcome in the art. For example, increased processing of diamond into various tools and workpieces would be permitted.
Another valuable property of diamond is its compressive fracture strength. Compressive fracture strength measures the mechanical strength of a diamond crystal and is the static force required to break (or fracture) the crystal. Compressive fracture strength is a quantifiable mechanical property of diamond grit. Typically, hundreds of grit are tested and the average force recorded to break the grit is used as the compressive fracture strength of that particular grit product. Heretofore, etching of diamond grit for one hour in molten potassium nitrate at 870.degree. K was reported to increase the strength of the diamond grit due to the removal of surface roughness and defects (See pp. 489-490, The Properties of Natural and Synthetic Diamond, Ed. by J. E. Field, 1992).